31st Regiment or 31st Infantry Regiment may refer to:
Infantry regiments
31 Combat Engineer Regiment (The Elgins), a unit of the Canadian Army
31st Infantry Regiment (Thailand), a unit of the Royal Thai Army
31st (Huntingdonshire) Regiment of Foot, a unit of the United Kingdom Army
31st Infantry Regiment (United States), a unit of the United States Army
Cavalry regiments
31st Mechanized Infantry Regiment "Asturias", a unit of the Spanish Army
31st Cavalry Regiment (United States), a unit of the United States Army
Artillery regiments
31st Reserve Field Artillery Regiment (Ireland), a unit of the Irish Army
Combat support regiments
31 (City of London) Signal Regiment, a unit of the United Kingdom Army
American Civil War regiments
31st Illinois Volunteer Infantry Regiment
31st Iowa Volunteer Infantry Regiment
31st New York Volunteer Infantry Regiment
31st Infantry Regiment, United States Colored Troops
31st Wisconsin Volunteer Infantry Regiment
See also
31st Division (disambiguation) 31st Group (disambiguation) 31st Brigade (disambiguation) 31st Battalion (disambiguation) 31st Squadron (disambiguation)